1. Field of the Invention
This application is based on application No. MI96 A 002595 filed in Italy, the content of which is incorporated hereinto by reference.
The present invention relates to a scanning reader of an optical code placed on an article in movement and a method of scanning said optical code by means of said reader.
2. Discussion of Prior Art
The term "optical code" is intended to mean a set of graphic markings (placed on a label or directly on a product or on any other support) by means of which a piece of information is coded as a sequence of white areas and black areas or of variously coloured areas, arranged according to one or more directions. Examples of such codes are the bar codes, the two-dimensional codes, the colour codes and the like.
Generally, a scanning reader of an optical code placed on an article in movement comprises a source of light capable of generating a beam of coherent light and suitable optical components capable of focusing the light beam on the code, forming a scanning line. The light diffused by the optical code, consisting of a series of impulses, is directed to a photodetector that emits electrical signals representative of the detected light. The electrical signals are decoded in an electrical or electronic circuit that provides data capable of describing the optical code.
If the optical code is of the bar type, as is commonly the case, in order to read it correctly, the light beam is focused on the code so that the projection of its cross-section on the code has precise dimensions, determined by the thickness of the bars of the code. In fact, the reading of the code would be incorrect if the cross-section of the light beam were to cover more than two bars.
In a number of cases the article is transported by a conveyor belt and the reader is located along the path of the article so as to be able to read the optical code that is applied in a random position on one of its walls. If the optical code is on a side wall, substantially parallel to the direction of movement of the article, the optical code reader is placed in front of such wall. The beam of scanning light has a direction that is substantially orthogonal to the wall on which there is the optical code and, whatever the position of the optical code with respect to the wall, on the top, on the bottom, in the centre or on the sides, the reading does not exhibit any problems. On the other hand, if the optical code is placed on a front or rear wall of the article, substantially orthogonal to the direction of movement, the reader is placed above the conveyor belt and, thus, above the front or rear wall on which there is the code and the article, with its movement, gets closer to it or moves away from it. The beam of scanning light has a direction oblique with respect to the optical code and it is difficult to make a sufficient number of useful scans while the article is in the range of depth of the light beam that, generally, is fairly narrow.